<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 500px;
            height: 300px;
            border-width: 10px;
            border-style: solid;
            border-color: green;
        }
    </style>
</head>

<body>
    <div class="test">
        我是div
    </div>
</body>

</html>